Epilepsy is defined as a disorder characterized by recurring seizures, typically manifested by motor, sensory, and/or cognitive malfunction with or without unconsciousness. Motor convulsions are the most common symptom that arises from epilepsy. Convulsive motor attacks can be highly disruptive to normal every day life. Another major category of seizures is the absence seizure, which is a seizure of the brain with little obvious motor movement in its purest form. The occurrence of a seizure with a motor and/or an absence component can be monitored in two ways.
First, the gross motor activity of the patient is typically measured by an electromyograph (EMG) to provide an EMG waveform. An electromyograph operates by monitoring the electrical response of a muscle, in the form of a voltage, to movement. A record of these voltage variations, the EMG waveform, is taken over time. EMG waveforms are made using a mechanical EMG recorder that employs pens to record the analog voltage fluctuations on a strip of paper. As a continuous chart of paper is moved beneath an array of galvanometer driven ink pens, the pens trace out the muscle activity as a series of wavy or jagged lines.
The motor seizure is also typically accompanied by heightened brain activity and thus, an electroencephalograph (EEG) may be used to monitor the seizure by providing an EEG waveform. Further, because the EEG measures brain activity, the EEG can also be used to monitor absence seizures. Similar to an EMG, an EEG monitors brain activity by measuring the very small voltage fluctuations that are generated in the brain, which are detected by electrodes typically attached to a patient's scalp. To aid in studying these analog signals, a record of the voltage fluctuations, the EEG waveform, is often made over time. Traditionally, EEG waveforms are made using a mechanical EEG recorder that employs pens to record the analog voltage fluctuations on a strip of paper. As a continuous chart of paper is moved beneath an array of galvanometer-driven ink pens, the pens trace out the brainwave activity as a series of wavy or jagged lines.
Recently, digital EEGs and EMGs have been developed. Instead of printing the EEG waveforms or EMG waveforms on paper, digital recorders convert sensed analog waveforms into digital signals that are stored in some digital storage medium such as random access memory. (RAM), hard disks, storage tapes, etc. The stored digital waveforms can then be transferred to a digital reader for display and analysis by medical personnel. A digital reader can consist of a personal computer including memory, a processor, input devices and an electronic display screen, e.g., a cathode ray tube (CRT) monitor, for displaying the waveforms.
The information provided by EEGs and EMGs have been used in the prior art to determine if a seizure has taken place or is in progress. However, to date, these methods have proved to be less than convenient or cost effective for daily monitoring. It can be appreciated that it is important to be able to determine when a seizure has occurred, and, by early detection of the onset of a seizure, prevent the seizure. The present invention describes a method and apparatus for detecting seizures in epileptics.